72 115hp no reverse

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ajkustra

Seaman Apprentice
Joined
Aug 17, 2012
Messages
30
I recently bought a used gear box, replaced the impeller, and installed it. It seems to be ok, but i have no reverse. When i installed it i put the shifter in neutral and the box in neutral because i couldn't get the shifter splines lined up any other way. In forward it works great, neutral is free spinning, and in reverse the prop will turn about one third turn each way with motor off, as it should i think. But in the water the prop seems to spin while in reverse but there is no thrust. Any ideas? Forward and neutral work fine in the water.
 
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Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,158
Re: 72 115hp no reverse

Likely a simple shift cable adjustment. Remove the throttle and shift cables from the clamp. Rotate the brass adjustment barrell nut to push the shift slide a bit more to the rear of the motor. Test carefully at low speeds until you are sure it is adjusted correctly.
 
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ajkustra

Seaman Apprentice
Joined
Aug 17, 2012
Messages
30
Re: 72 115hp no reverse

Thanks a ton Chris, I'll try that when it stops raining later this week.
 
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ajkustra

Seaman Apprentice
Joined
Aug 17, 2012
Messages
30
Re: 72 115hp no reverse

Chris, I tried the adjustment process, No luck. It's positively engaging in reverse, and the prop spins in the water but the boat moves extremely slowly (maybe prop is not spinning as quickly as it should prop rpm vs. engine rpm.) I'm thinking my problem is inside the lower unit, unless i put the LU on with the shifter one or two splines off? I put it on with the shifter handle/cable in N, and the gearbox in N. When rotating the shifter shaft on the box by hand, neutral has a pretty positive detent so I think the cable/box are correctly aligned. Another issue may be that the reverse lock doesn't work, will this keep me from moving?
 
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Chris1956

Supreme Mariner
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Mar 25, 2004
Messages
27,158
Re: 72 115hp no reverse

reverse lock will have no effect, as it simply holds motor in vertical position. I do not think a prop could slip on it's hub in reverse only, so it is probably good. Can you observe prop rotating with boat in water? If so, have helper advance throttle in reverse and see what happens. Maybe prop ventilates, or control box never advances throttle in reverse? Strange issue...
 
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ajkustra

Seaman Apprentice
Joined
Aug 17, 2012
Messages
30
Re: 72 115hp no reverse

The prop definetly spins in reverse gear, and the motor revs up. Possible ventilatiing? Would a whle.tale help? Ihave one but.not mounted.
 
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Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,158
Re: 72 115hp no reverse

Not sure whale tail would help. likely ventilation would just continue, if that is what is happening. Best to visually inspect under power, and see if she ventilates.

Before water test, remove wrap cowl and see if throttle actually advances (motor off), in reverse. Maybe issue is in MerControl.
 
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